As moistureproof papers, tarpaulin papers and wax papers were formerly known. At present, papers having a high-molecular weight compound, such as polyethylene, polypropylene and polyvinyl chloride, coated or laminated thereon to impart moistureproof and waterproof properties are generally used. However, while the above-described moistureproof papers could thoroughly exhibit the function with respect to the moistureproof properties, they were extremely poor in defibration properties at the time of collection and reuse as a waste paper were difficult. For this reason, a big problem still remained from the view-points of saving of natural resources, effective use, and the like.
As papers which solve the above-described defects and are superior in moistureproof and waterproof properties and defibration properties as waste papers and processes for producing the same, those using a wax-based emulsion alone or a mixed solution of a wax-based emulsion with a synthetic rubber-based latex (refer to the official gazette of Patent Publication No. 3-10759), those using a mixed solution of an acrylic emulsion with a wax-based emulsion (refer to the official gazette of Patent Publication No. 2-1671 and the official gazette of Patent Application Laid-Open No. 6-200498), and the like are known. However, while the moistureproof and waterproof papers produced by each of these processes provided a capacity comparable to the existing moistureproof papers with respect to the moistureproof and waterproof properties, they were not satisfactory in obtaining other necessary qualities.
For example, moistureproof papers obtained by coating a wax-based emulsion involved such defects that they cause a reduction in the coefficient of friction, they are very inferior in moistureproof properties when folded, and that when they are reused waste-paper stock, a large amount of the wax contained in the waste-paper stock adheres to rolls and the like of a paper machine to generate roll stains, whereby the recycling properties are greatly deteriorated. The moistureproof papers produced by coating a mixture of a synthetic rubber-based latex with a wax-based emulsion as disclosed in the official gazette of Patent Publication No. 3-10759 were very inferior in the heat-sealing capacity which is required for sealing and further not satisfactory yet in the defibration properties as the collection properties of waste papers. Further, inferiority in the heat-sealing capacity entails use of gummed tapes or adhesives such as those using vinyl acetate for sealing of wrapping papers. For this reason, the tape or adhesive adheres to the moistureproof paper sealed by such materials and adversely affects the defibration properties at the time of recycling, resulting in a big obstacle for the reuse from the standpoint of practical use.
In addition, the moistureproof papers produced by coating a mixture of an acrylic emulsion with a wax-based emulsion as disclosed in the official gazette of Patent Publication No. 2-1671 and the official gazette of Patent Application Laid-Open No. 6-200498 involved the following defects. In the official gazette of Patent Publication No. 2-1671, the heat-sealing properties and defibration properties are not at all mentioned. Also, the amount of the wax-based emulsion used was so high as from 90:10 to 50:50, (preferably 70:30 to 60:40) in terms of a mixing ratio of the acrylic resin to the wax as a solids content, resulting in a reduction in the coefficient of friction of moistureproof papers, and the paper-making properties were not yet satisfactory at the time of collection as waste papers for reuse. Thus, the moistureproof papers produced in this patent were not practically useful. Further, in the official gazette of Patent Application Laid-Open No. 6-200498, while the heat-sealing properties were good, the amount of the wax-based emulsion used was so high as in the case of above mentioned from 100:30 to 100:60 in terms of a mixing ratio of the acrylic resin to the wax as a solids content, resulting in a reduction of the coefficient of friction of moistureproof papers, and the defibration properties and paper-making properties were not satisfactory.
On the other hand, as moistureproof papers having light-proofing properties, moistureproof papers produced by laminating an aluminum foil and a polyolefin-based resin on a base paper, those produced by laminating a polyolefin-based resin containing a carbon black on a base paper, those produced by laminating a polyolefin-based resin on a black base paper which is prepared by subjecting a paper to paper making with carbon black, etc. have hitherto been used. However, any of these moistureproof papers were extremely poor in the defibration properties at the time of collection as waste papers for reuse, could not be reused, and had to be disposed by burning or reclamation as industrial wastes.
As papers which solve the above-described defects and are superior in light-proofing properties, moistureproof properties, and the defibration properties and processes for producing the same, those coating a mixed solution of an acrylic emulsion with a wax-based emulsion on the surface of a base paper prepared by subjecting a paper to paper making with an inorganic pigment such as carbon black, or of a base paper having a coated layer of an inorganic pigment such as carbon black or a metallized layer of an aluminum paste or the like provided thereon (refer to the official gazette of Patent Application Laid-Open No. 6-184987), those provided with a light-proofing layer containing an inorganic pigment such as carbon black and an aluminum paste as a major component, and a moistureproof layer containing an acrylic emulsion and a wax-based emulsion on a paper support (refer to the official gazette of Patent Application Laid-Open No. 7-82691), etc. are known. However, while the moistureproof papers having light-proofing properties produced by each of these processes provided the defibration properties for separating the base paper in a fibrous state, they were not satisfactory in the paper-making properties at the time of collection as waste papers for reuse and hence, were not practically useful.
For example, in those using carbon black, the carbon black can not be removed without using a deinking step. Accordingly, for example, in general manufacturers of corrugated papers having no deinking step, the carbon black standed out on the surface of a recycled paper, which resulted in a reduction of the commercial value of the recycled paper and made it impossible for practical reuse. Also, in those using an aluminum paste, the aluminum powder can not be removed even in the deinking step. Accordingly, the aluminum powder was mingled into a recycled paper so that the recycled paper could not be practically used.
Further, with respect to the mixture of an acrylic emulsion with a wax-based emulsion which is used for the purpose of imparting moistureproof properties, the amount of the wax-based emulsion used is so high as from 100:30 to 60 as disclosed in the invention of the official gazette of Patent Application Laid-Open No. 6-184987 and from 40:60 to 90:10 as disclosed in the invention of the official gazette of Patent Application Laid-Open No. 7-82691, respectively in terms of a mixing ratio of the acrylic resin to the wax-based emulsion as a solids content. Thus, roll stains were likely generated at the time of reuse of waste papers, and the recycling properties were not satisfactory yet.
Moreover, in those using carbon black, the surfaces thereof are so black that it is impossible to undergo printing or letter printing. Accordingly, in order to improve the printability, it was necessary to undergo whitening processing, processing of laminating a printable paper, or the like.
Incidentally, as papers which solve the above-described defects and are superior in the light-proofing properties, the moistureproof properties, and the recycling properties and processes for producing the same, those provided with a light-proofing layer containing a yellow pigment such as Benzidine Yellow and the like as major components and a moistureproof layer containing a synthetic rubber-based latex or a resin-based latex and a wax-based emulsion on a paper support (refer to the official gazette of Patent Application Laid-Open No. 7-1676) are known. However, the light-proofing properties obtained by this process were limited to from 250 to 500 nm in terms of the light-sensitive wavelength of diazo light-sensitive materials necessary as a wrapping material of presensitized (PS) printing plates but did not screen lights in a wide wavelength region ranging from ultraviolet rays to infrared rays as seen in an aluminum foil and carbon black.